Currently drivers for ACPI enumerated devices that have their interrupt
line connected to a GPIO controller instead of IO-APIC are required to do
complete gpiod_get()/gpiod_to_irq() etc. dance themselves. This adds
unnecessary lines of code to these drivers.

It turned out that DT solved the problem already with introduction of
of_irq_get() which is able to handle GPIO based interrupts as well through
irqchip API [1].

Following two patches does the same for ACPI by introducing new function
acpi_dev_gpio_irq_get() that is then used in I2C core to automatically
translate ACPI GpioInt resource to Linux IRQ number.

This requires that the boot firmware (BIOS/coreboot) configures these pins
correctly (input, etc) before handing over to OS. I've tested this on Intel
Baytrail, Braswell and Skylake based machines where this is true.